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Urban, agriculture and coal mining land use/cover impacts upon aquatic habitat, toxicity and biodiversity were investigated in Leading Creek, a 388 km2 watershed in southeastern Ohio. Abandoned strip mine land (ASML) and active deep underground mines were examined along with abandoned near-surface underground mine land (AUML). The work focused on assessment of aquatic toxicity, water quality, and biodiversity through investigation of associated ecological responses for both treated and untreated AMD. Relations were examined among land use/cover, chemistry, and various ecological and toxicological endpoints. Sources of data (scale 1:24000) included Landsat5 imaging from 1988 and 1994, and directly digitized extents of underground mining activities dating to the 19th century, with more recently created strip mines. USEPA and Ohio EPA qualitative habitat scoring protocols were used. Land use/cover thresholds were established using ASML=3%, AUML=2% to 10%, Urban=3% to 5%, and Bare Soil=3%. Biodiversity was assessed using qualitative benthic macroinvertebrate taxon richness and abundance, for total and EPT groups, respectively. A better understanding of acid mine drainage (AMD) was demonstrated linking land use/cover, coal bed, sediment, and water column chemistry to aquatic ecotoxicity through examination of the origin and fate of sulfate, magnesium, iron, manganese, and zinc. Key findings in risk assessment of Leading Creek indicated that (1) abandoned near-surface underground mine lands (AUML) were associated with >90% of untreated AMD reaching Leading Creek; (2) degradation to aquatic ecology was primarily associated with water quality degradation due to AMD, not with sediment quality degradation; (3) modest habitat destruction, especially sedimentation effects, were observed for ASML>3%, and urbanization>5% in small subsheds; (4) unique chemical signatures differentiated mining techniques instream; and (5) in situ Corbicula fluminea growth rates were dependent upon drainage area. Sporadic signs of agricultural and urban impacts were indicated from acute toxicity with Ceriodaphnia dubia and chronic in situ toxicity testing with C. fluminea. Both the ecotoxicological tests were shown to be reliable indicators of AMD impact from AUML, on watershed and subwatershed scales. AMD was strongly associated with depressed biodiversity, low pH, and elevated zinc. Ecotoxicity monitoring supported interconnections found between sediment and water chemistry, land use/cover, and biodiversity. / Ph. D.

This dissertation reports the design of a process (patent pending) to remove iron from acid mine drainage (AMD) without the formation of metal hydroxide sludge. The system includes the oxidation of ferrous iron in a packed bed bioreactor, the precipitation of iron within a fluidized bed, the removal of manganese and heavy metals (Cu, Ni, Zn) in a trickling filter at high (>9) pH, with final neutralization in a carbonate bed. The technique avoided the generation of iron oxyhydroxide sludge. In the packed bed bioreactor, maximum substrate oxidation rate (R_,max) was 1500 mg L⁻¹ h⁻¹ at dilution rates of 2 h⁻¹, with oxidation efficiency at 98%. The half-saturation constant (similar to a Ks) was 6 mg L⁻¹. The oxidation rate was affected by dissolved oxygen below 2 mg L⁻¹, with a Monod-type Ko for DO of 0.33 mg L⁻¹. Temperature had a significant effect on oxidation rate, but pH (2.0 to 3.25) and supplemental CO₂ did not affect oxidation rates. Iron hydroxide precipitation was not instantaneous when base was added at a OH/Fe ratio of less than 3. Induction time was found to be a function of pH, sulfate concentration and iron concentration, with a multiple R² of 0.84. Aqueous [Al (III)] and [Mn (II)] did not significantly (α = 0.05) affect induction time over the range of concentrations investigated. When specific loading to the fluidized bed reactor exceeded 0.20 mg Fe m⁻² h⁻¹, dispersed iron particulates formed leading to a turbid effluent. Reactor pH determined the minimum iron concentration in the effluent, with an optimal at pH 3.5. Total iron removals of 98% were achieved in the fluidized bed with effluent [Fe] below 10 mg L⁻¹. Further iron removal occurred within the calcium carbonate bed. Heavy metals were removed both in the fluidized bed reactor as well as in the trickling filter. Oxidation at pH >9 caused manganese to precipitate (96% removal); removals of copper, nickel, and zinc were due primarily to sorption onto oxide surfaces. Removals averaged 97% for copper, 70% for nickel and 94% for zinc. The treatment strategy produced an effluent relatively free of iron (< 3 mg/L), without the formation of iron sludge and may be suitable for AMD seeps, drainage from acidic tailings ponds, active mine effluent, and acidic iron-rich industrial wastewater. / Ph. D.

Although mining is essential to life in our modern society, it generates huge amounts of waste that can lead to acid mine drainage (AMD). Most of these mine wastes occur as large piles that are open to the atmosphere so that air and water vapor can circulate through them. This study addresses the reactions and transformations of the minerals that occur in humid air in the pore spaces in the waste piles. The rate of pyrite oxidation in moist air was determined by measuring over time the change in pressure between a sealed chamber containing pyrite plus oxygen and a control. The experiments carried out at 25?C, 96.8% fixed relative humidity, and oxygen partial pressures of 0.21, 0.61, and 1.00 showed that the rate of oxygen consumption is a function of oxygen partial pressure and time. The rates of oxygen consumption fit the expression (dn/dt=(3.31x10^-7)(P^0.5)(t^-0.5) It appears that the rate slows with time because a thin layer of ferrous sulfate + sulfuric acid solution grows on pyrite and retards oxygen transport to the pyrite surface. The transformation of efflorescent sulfate minerals (the reaction products of iron sulfide oxidation) from a pyrrhotite-rich massive sulfide is explained using a systematic analysis of their stoichiometry and thermodynamics. Their stabilities are controlled by oxygen partial pressure, relative humidity, and activity of sulfuric acid and can be visualized using log activity of oxygen-log activity of water and log acitvity of sulfuric acid-log activity of water diagrams developed during this study. Samples from the field site were analyzed in the laboratory to determine mineralogy, equilibrium relative humidity, chemical composition, and acid generation potential. Dissolution experiments showed that fibroferrite-rich samples had the highest acid producing potential, followed by copiapite-rich samples and then halotrichite-rich samples. The most abundant metals in solutions produced by dissolving the salts were magnesium, aluminum, zinc, copper, calcium, and lead. The molar concentrations of the metals varied with mineralogy. However, all of these minerals release metals and acid when they dissolve and therefore represent a significant environmental threat. / Ph. D.

Rare earth elements (REE) exhibit particular and unique properties that render them essential to technological applications. Of particular interest is their involvement in the transition toward global sustainability and their military applications. The magnetic properties of the rare earth elements is of primordial importance to sustainable development. More specifically, terbium and dysprosium are two elements with no known substitutes in critical applications and with no domestic or allied sourcing available. These elements are currently mined by in-situ leaching of ion-absorbed clays, mostly from illegal operations in Myanmar financed by Chinese companies. The demand from both elements, and for the other magnet rare earths is projected to growth at very high rates through 2035 while the world undergoes a transition toward sustainability, and a drastic reduction in greenhouse gases emissions. Our team has been evaluating the potential of acid mine drainage (AMD) as a source of rare earth elements and critical materials (CM). Acid mine drainage is the result of in-situ generation of sulfuric acid due to the weathering of sulfide ores. It is a significant legacy environmental issue and one of the largest pollutants in many mining districts throughout the world. The objective of the present work is to provides a roadmap for the utilization of AMD as a critical material feedstock to preserve the independence of the United States of America with regards to these materials. To that effect, a fundamental economic assessment of REE/CM recovery from AMD using a network sourcing strategy in addition to a robust, flexible feedstock separations and refining facility was undertaken. A techno-economic analysis of the extraction, refining, separation and reduction to metal is presented along with a sensitivity analysis.The results of this analysis show that, with the exception of the minimum price scenario, all operational configurations have positive economic indicators with rates of return varying from 25% to 32% for the contemporary price scenario. This is primarily due to the very high enrichment in terbium and dysprosium of AMD. The optimal configuration was determined to be production of Co, Mn, and all REEs except for mischmetal, which is not recovered. Sensitivity analysis and Monte Carlo Simulation show that capital cost and HCl consumption are the two major factors influencing rate of return, thus indicating opportunities for future technology development and cost optimization. In order to reduce both the capital and operation cost of the facility, alternative ionic liquids extractants based on conventional acidic extractants where synthesized and investigated. The results show that the ionic liquids varied in performance, with [c101][D2EHP] and [c101][EHEHP] performing poorer than their conventional counterparts and [c101][c572] performing better. The performance of [c101][c572] was 13% superior to Cyanex 572, 20% superior to EHEHPA and 27% superior to D2EHPA the current commercially used extractants. Recommendations for further study on [c101][c572] include stripping tests, continuous pilot testing, and techno-economic analysis. The test work revealed that zinc and to a lesser extent calcium were significant deleterious elements in the solvent extraction circuit, and that selective removal would significantly reduce the acid-base consumption of the separation circuit. A process was developed to selectively remove calcium and zinc from AMD-derived feedstock and from REE products. The ammonium chloride leach process offer many advantages, including the possibility of closing the cycle by using carbon dioxide sequestration as a step to regenerate the ammonium chloride in a zero-discharge process. / Doctor of Philosophy / A younger me: - What are these elements in the bottom of the periodic table? My high school chemistry teacher: - "Don't waste time there, these are of no concern." Twenty years later, technological developments and the imperative to transition away from fossil energy to mitigate climate change have brought the rare earth elements, a series of 17 elements with unique properties to the forefront of the conversation. In addition to an organic increase in demand, the recent supply chain consolidation by China is adding a geopolitical risk to the equation. The magnetic properties of the rare earth elements is of primordial importance to sustainable development and to our military technology. More specifically, terbium and dysprosium are two elements with no known substitutes in critical applications and with no domestic or allied sourcing available. These elements are currently mined from illegal operations in Myanmar, with the support of Chinese companies. The demand from both elements, and for the other magnet rare earths is projected to growth at very high rates through 2035 while the world undergoes a transition toward sustainability, and a drastic reduction in greenhouse gases emissions. Given the important of the rare earth elements, and the absence of significant deposits in the united states, with the exception of the Bear Lodge and Elk Creek deposits, the Department of Energy has mandated academic institution of evaluating alternative sources of rare earth elements. Our team has been evaluating the potential of acid mine drainage as a source of rare earth elements and critical materials. Our team has surveyed many acid mine drainage sources and determined that many sites are highly enriched in terbium and dysprosium. Acid mine drainage is a legacy environmental issue related to past problematic mine development techniques. In the problematic mines. these acidic mine waters are permanently generated and if not treated can have severe impacts on water streams in which they flow. The toxicity of the acid mine drainage on the environment is due to its high acidity and significant levels of toxic metals. Acid mine drainage can be recognized by their yellow to red tint. It is treated by reacting it with a neutralization agent, which results in treated water and a sludge. The sludge is dewatered and stored in tailing impoundments. I have designed a process for the economical recovery of rare earth elements and critical materials from acid mine drainage. The cost to build and operate the facility was derived and it was determined that the project could be further enhanced by reducing the plant chemical reagent consumption. One specific category of chemical referred to as extractant, is central to the rare earth separation process. A novel variation on the standard extractants has been evaluated and promises to provide significant savings. While the extractants were investigated, it was noticed that some impurities such as zinc and calcium created issues in the circuit. I then developed a process for their selective removal. The process also provide a net carbon dioxide sequestration potential.